Ojalá is a beautiful and unique Spanish word that expresses a strong desire or hope, often for something that is unlikely or impossible. It's similar to saying "I wish" or "If only" in English.
In "Corazón De Piedra," Ángela Aguilar uses "Ojalá" to convey deep regret and longing, singing, "Ojalá existiera regresar el tiempo" (I wish it were possible to go back in time) and "Ojalá pudiera regresar el tiempo" (If only I could go back in time). This word perfectly captures the song's theme of wishing to undo past pain and relive cherished moments.
The title is the plan, and the plan does not hold. Ángela Aguilar wants a corazón de piedra para no sentir ("a heart of stone so I feel nothing"), and then spends the rest of the song feeling all of it anyway: No lo puedo evitar, cierro los ojos y ahí estás ("I can't help it, I close my eyes and there you are").
There is no betrayal in it, which is what makes the complaint sting. What she holds against him is the distance between what he said and what he did: Tus labios decían, 'te amo' / Pero te faltó demostrar ("your lips were saying 'I love you', but you never showed it"). Then listen to what she actually asks for. She wants the time back, and not to fix anything with it: Para escuchar ese último, 'te quiero' ("to hear that last 'I love you'"). She would rather replay the goodbye than rewrite it.